Java操作FreeMarker模板引擎的基本用法示例小结

FreeMarker 是一个采用 Java 开发的模版引擎，是一个基于模版生成文本的通用工具。 它被设计用来生成 HTML Web 页面，特别是基于 MVC 模式的应用程序。虽然使用FreeMarker需要具有一些编程的能力，但通常由 Java 程序准备要显示的数据，由 FreeMarker 生成页面，并通过模板显示准备的数据。
http://freemarker.org/

public void process(String template, Map<String, ?> data) throws Exception {
  Configuration cfg = new Configuration();
  cfg.setDirectoryForTemplateLoading(new File("ftl"));
  cfg.setObjectWrapper(new DefaultObjectWrapper()); 

  //设置字符集
  cfg.setDefaultEncoding("UTF-8"); 

  //设置尖括号语法和方括号语法,默认是自动检测语法
  // 自动 AUTO_DETECT_TAG_SYNTAX
  // 尖括号 ANGLE_BRACKET_TAG_SYNTAX
  // 方括号 SQUARE_BRACKET_TAG_SYNTAX
  cfg.setTagSyntax(Configuration.AUTO_DETECT_TAG_SYNTAX); 

  Writer out = new OutputStreamWriter(new FileOutputStream(FILE_DIR + template + ".txt"),"UTF-8");
  Template temp = cfg.getTemplate(template);
  temp.process(data, out);
  out.flush();
}

0、使用freemarker制作HelloWord web页面
新建一个WEB工程，并导入freemarker.jar，在WEB-INF下新建文件夹templates用于存放模版文件，在templates下新建test.ftl，这是示例模版文件。内容就是HTML内容，里面带有一个标记符，用于将来进行变量替换，内容如下：

<html>
 <head>
    <title>freemarker测试</title>
  </head>
  <body>
    <h1>${message},${name}</h1>
  </body>
</html>

新建一个Servlet，用于请求设置变量，并处理模版的输出：

package com.test.servlet;
import java.io.IOException;
import java.io.Writer;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import freemarker.template.Configuration;
import freemarker.template.Template;
import freemarker.template.TemplateException;
@SuppressWarnings("serial")
public class HelloFreeMarkerServlet extends HttpServlet {
  // 负责管理FreeMarker模板的Configuration实例
  private Configuration cfg = null;
  public void init() throws ServletException {
    // 创建一个FreeMarker实例
    cfg = new Configuration();
    // 指定FreeMarker模板文件的位置
    cfg.setServletContextForTemplateLoading(getServletContext(),
        "/WEB-INF/templates");
  }
  @SuppressWarnings("unchecked")
  public void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    // 建立数据模型
    Map root = new HashMap();
    root.put("message", "hello world");
    root.put("name", "java小强");
    // 获取模板文件
    Template t = cfg.getTemplate("test.ftl");
    // 使用模板文件的Charset作为本页面的charset
    // 使用text/html MIME-type
    response.setContentType("text/html; charset=" + t.getEncoding());
    Writer out = response.getWriter();
    // 合并数据模型和模板，并将结果输出到out中
    try {
      t.process(root, out); // 往模板里写数据
    } catch (TemplateException e) {
      e.printStackTrace();
    }
  }
  public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    doPost(request, response);
  }
  public void destroy() {
    super.destroy();
  }
}

注意要在你的web.xml中配置该Servlet：

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
  http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <servlet>
    <servlet-name>hello</servlet-name>
    <servlet-class>
      com.test.servlet.HelloFreeMarkerServlet
    </servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>hello</servlet-name>
    <url-pattern>/hello</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

为了方便测试，访问工程直接跳转到Servlet，对主页index.jsp做一个简单修改：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()
+":"+request.getServerPort()+path+"/";
%>
<html>
 <body>
  <%
  String mypath = "hello";
  response.sendRedirect(basePath + mypath);
  %>
 </body>
</html>

部署工程到Tomcat，启动并访问http://localhost:8080/f ，这里我建立的工程名称就是 f 。

1、计算式

<#-- 1、算术运算 -->[BR]
${3 + 4} 

<#-- 2、内建函数 -->[BR]
${"rensanning"?upper_case}

2、输出一个值

HashMap t2root = new HashMap<String, String>();
t2root.put("user", "RenSanNing"); 

${user}, Welcome!

3、输出一个列表

Map<String, Object> t3root = new HashMap<String, Object>();
List<Food> menu = new ArrayList<Food>();
menu.add(new Food("iText in Action", 98));
menu.add(new Food("iBATIS in Action", 118));
menu.add(new Food("Lucene in Action", 69));
t3root.put("menu", menu); 

<#list menu as food>
${food.name} ${food.price?string.currency}
</#list>

4、逻辑判断（IF,SWITCH)

Map<String, Object> t4root = new HashMap<String, Object>();
t4root.put("x", 2);
t4root.put("y", "medium");

<1>if, else, elseif:
<#if x == 1>
 x is 1
<#elseif x == 2>
 x is 2
<#elseif x == 3>
 x is 3
<#elseif x == 4>
 x is 4
<#else>
 x is not 1 nor 2 nor 3 nor 4
</#if> 

<2>switch, case, default, break:
<#switch y>
 <#case "small">
   This will be processed if it is small
   <#break>
 <#case "medium">
   This will be processed if it is medium
   <#break>
 <#case "large">
   This will be processed if it is large
   <#break>
 <#default>
   This will be processed if it is neither
</#switch> 

<3>list, break:
<#assign seq = ["winter", "spring", "summer", "autumn"]>
<#list seq as x>
 ${x_index + 1}. ${x}<#if x_has_next>,</#if>
</#list>

5、自定义函数

<#function fact n>
 <#if n == 0>
  <#return 1 />
 <#else>
  <#return fact(n - 1) * n />
 </#if>
</#function> 

<#list 0..10 as i>
 ${i}! => ${fact(i)}
</#list>

6、定义变量

<#-- 1、本地变量 -->[BR]
<#function partg n lst>
 <#local ans = []>
 <#list lst as x>
  <#if (x >= n)>
   <#local ans = ans + [x]>
  </#if>
 </#list>
 <#return ans>
</#function> 

<#assign ls = [10, 2, 4, 5, 8, 1, 3]>
<#list partg(4, ls) as x>${x} </#list> 

<#-- 2、变量域测试 -->[BR]
<#macro test>
  03. ${x}
  <#global x = "global2">
  04. ${x}
  <#assign x = "assign2">
  05. ${x}
  <#local x = "local1">
  06. ${x}
  <#list ["循环1"] as x>
    07. ${x}
    <#local x = "local2">
    08. ${x}
    <#assign x = "assign3">
    09. ${x}
  </#list>
  10. ${x}
</#macro> 

<#global x = "global1" />
01. ${x}
<#assign x = "assign1" />
02. ${x}
<@test />
11. ${x}

7、定义宏macro

<#-- 1、无参数 -->[BR]
<#macro greet>
Welcome!
</#macro> 

<@greet /> 

<#-- 2、有参数 -->[BR]
<#macro greet user>
${user}, Welcome!
</#macro> 

<@greet user="RenSanNing"/> 

<#-- 3、有多个参数 -->[BR]
<#macro table cols rows>
 <table>
  <#list 1..rows as row>
   <tr>
    <#list 1..cols as col>
     <td>${row}, ${col}</td>
    </#list>
   </tr>
  </#list>
 </table>
</#macro> 

<@table cols=3 rows=2 /> 

<#-- 4、中间跳出 -->[BR]
<#macro out>
 显示文字
 <#return>
 不显示文字
</#macro> 

<@out /> 

<#-- 5、嵌套 -->[BR]
<#macro lprint lst>
 <#list lst as item>
 ・${item}<#nested item />
 </#list>
</#macro> 

<@lprint 1..3; x>^2 = ${x * x}</@lprint>
<@lprint 1..3; x>^3 = ${x * x * x}</@lprint>
<@lprint ["Let's go", "to the", "land of Medetai"] />

8、include

<#include "T108include.ftl">
${url}
<@greet name="rensanning" />

T108include.ftl

<#macro greet name>
${name}, Welcome!
</#macro> 

<#assign url="http://www.baidu.com/">

9、名字空间

<#import "T109include.ftl" as my>
<#assign url="http://www.google.com/"> 

${my.url}
<@my.greet name="rensanning" /> 

${url}

T109include.ftl

<#macro greet name>
${name}, Welcome!
</#macro> 

<#assign url="http://www.baidu.com/">

10、自定义指令Directive

public class SystemDateDirective implements TemplateDirectiveModel { 

  public void execute(Environment env, Map params, TemplateModel[] loopVars,
      TemplateDirectiveBody body) throws TemplateException, IOException {
    Calendar cal = Calendar.getInstance();
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
    env.getOut().append(sdf.format(cal.getTime()));
  } 

} 

public class TextCutDirective implements TemplateDirectiveModel {
  public static final String PARAM_S = "s";
  public static final String PARAM_LEN = "len";
  public static final String PARAM_APPEND = "append"; 

  @SuppressWarnings("unchecked")
  public void execute(Environment env, Map params, TemplateModel[] loopVars,
      TemplateDirectiveBody body) throws TemplateException, IOException {
    String s = getString(PARAM_S, params);
    Integer len = getInt(PARAM_LEN, params);
    String append = getString(PARAM_APPEND, params);
    if (s != null) {
      Writer out = env.getOut();
      if (len != null) {
        out.append(textCut(s, len, append));
      } else {
        out.append(s);
      }
    }
  }

....

Map<String, Object> t10root = new HashMap<String, Object>();
t10root.put("systemdate", new SystemDateDirective());
t10root.put("text_cut", new TextCutDirective());